1. Field of the Invention
This invention pertains generally to power line communication networks, and more particularly to an apparatus and method of establishing synchronization of streaming media devices communicating over a PLC network.
2. Description of Related Art
Power Line Communication (PLC) systems are being rapidly deployed in a number of consumer and business market segments in response to the convenience provided by this form of networking and aided by an increased availability of low-cost off-the-shelf PLC circuitry. PLC is a network technology in which consumer electronic devices are networked over conventional AC power connections. Recent enhancements in the available bandwidth has widened applications for PLC into streaming media (i.e. audio and video) networking arenas.
The first generation of these products were developed for Ethernet infrastructure replacement (i.e., local area networks, LANS). More recently, however, some vendors began to sell second-generation products, such as audio-streaming devices which allow conveyance of audio signals over the power lines from a source to a destination. Using the PLC network to share the audio signals is a convenient means of interfacing a plurality of streaming devices. In one example, separate audio devices can be distributed about a home or office environment wherein one device acts as the source of the audio information (e.g., CD player, MP3 player, and so forth) while the remaining devices are configured in a reception mode to receive the signal and output the audio.
However, one of the drawbacks with distributing audio over a localized area using this technique is that there is no synchronization between the audio output by a first device and by a second device. The lack of synchronization is primarily from two sources. First of all a delay is encountered as the digital signals are routed through the power lines. Secondly, each device exhibits a characteristic delay (i.e., fixed or variable) between the time the signal is received and the time an audio output is produced. In addition, the frequency of the clocks within each device can differ substantially as the clocks run independently. This lack of simultaneous output from the audio devices is termed herein as a lack synchronization between the devices.
It should be appreciated that even small synchronization differences between devices outputting audio (e.g., between a server which outputs audio and a client which outputs audio, between two clients which each output audio, or another combination of audio output devices) can begin to impact the fidelity of the resulting audio, depending on system layout, overlap, and so forth. The human hear can readily detect synchronization differences, referred to as the Haas effect, which exceed about thirty milliseconds (30 ms). The audio effect produced by the lack of synchronization, Haas effect, produces an “echo” wherein the audio sounds as if it were being played at the end of a tunnel, which can dramatically impair the overall audio experience. It should be appreciated that the synchronization problem arises for any audio outputs which are out of synchronization, such as the audio being output from nearby television sets, or from a television set and a separate audio system, which are subject to outputting the same audio stream. It should also be recognized that the problem is further exacerbated for audio being generated by surround sound systems and the like.
Accordingly, a need exists for a system and method of synchronizing the audio being communicated over a power line communication (PLC) network while overcoming the problems with device and communication path delays. These needs and others are met within the present invention, which overcomes the deficiencies of previously developed methods of assuring audio integrity.